X-Man is an equivalent of the regular Marvel Universe hero Cable, hailing from the “Age of Apocalypse” reality. He is the biological son of his dimension’s Scott Summers and Jean Grey, born of genetic tampering by Mr. Sinister. His first name is derived from his creator; Mr Sinister's real name: Nathaniel Essex and his last name from his genetic mother Jean Grey. Due to not being infected by a techno-organic virus as Cable was, X-Man achieved vast telepathic and telekinetic powers and was one of the most powerful mutants in existence during his lifetime.

X-Man was originally a four-issue mini-series replacing Cable during 1995’s “Age of Apocalypse” alternate reality storyline. However, Marvel transported Nate Grey to its regular shared universe after the storyline ended. Although derided by some for a concept perplexing to anyone not a diehard X-Men fan, the series ran until 2001, during which Nate struggled with being the most powerful person in a strange world. The series ended with his seemingly sacrificial death.

Despite his name, X-Man was only briefly a member of the X-Men, both in the Age of Apocalypse reality and in the regular reality. Initially the character was referred to only by his real name, both in the Age of Apocalypse and the primary Marvel universe. Shortly before the Onslaught crossover event, Nate began to be sporadically referred to as X-Man, without explanation for the in-universe origin of the code name.